The present invention relates to a technical field of a seat belt retractor mounted in a vehicle, such as an automobile, to retract webbing serving as a seat belt by a spool and a seat belt device that restrains an occupant with the seat belt withdrawn from the seat belt retractor. More particularly, the present invention relates to a technical field of a seat belt retractor including at least a vehicle sensor that inhibits withdrawal of a seat belt in case of an emergency, such as a vehicle collision when a deceleration much higher than a deceleration, which is produced during normal running, acts on a vehicle (hereinafter simply referred to as an emergency) and a webbing sensor that inhibits withdrawal of the seat belt when the seat belt is rapidly withdrawn at a speed higher than a normal seat belt withdrawing speed for wearing the seat belt (that is, an acceleration higher than a normal withdrawing acceleration for wearing the seat belt), and a seat belt device using the seat belt retractor.
A conventional seat belt device mounted on a vehicle seat of an automobile and the like restrains an occupant with a seat belt formed by webbing in case of an emergency. In general, such a seat belt device includes a seat belt retractor. Most conventional seat belt retractors include a vehicle sensor that operates to inhibit withdrawal of the seat belt in case of an emergency, and a webbing sensor that swings to inhibit withdrawal of the seat belt in response to the above-described rapid withdrawal of the seat belt (hereinafter referred to as rapid seat belt withdrawal).
For example, in a seat belt device which is mounted on a vehicle seat with no occupant sitting and in which a seat belt is not worn, a vehicle sensor is sometimes actuated by vibration during vehicle running. However, it is sometimes desired that, except when the occupant wears the seat belt, the vehicle sensor should not be actuated and the original function of the vehicle sensor for operating to inhibit withdrawal of the seat belt in case of an emergency should be cancelled (disabled). Accordingly, a seat belt retractor has been proposed in which the above-described original function of the vehicle sensor is performed when the occupant wears the seat belt and in which the original function of the vehicle sensor is cancelled (disabled) on a predetermined condition except when the occupant wears the seat belt (for example, see PTL 1 (U.S. Pat. No. 7,090,304), incorporated by reference herein).
The seat belt retractor described in PTL 1 includes a ring gear that corotates with a spool gear, and a control lever. Since the ring gear does not operate the control lever in a state in which the seat belt is withdrawn from the seat belt retractor by a predetermined length, the control lever allows a vehicle sensor to operate and perform its original function. Further, since the ring gear, which rotates with rotation of the spool in a seat belt retracting direction, operates the control lever, the control lever inhibits operation of the vehicle sensor and cancels the original function of the vehicle sensor in a state in which the spool at least fully retracts the seat belt.
In contrast, the webbing sensor sometimes operates to inhibit withdrawal of the seat belt from the seat belt retractor except during rapid seat belt withdrawal. For example, in a case in which the webbing sensor suddenly operates during full retraction of the withdrawn seat belt, a so-called end-lock sometimes occurs, that is, normal withdrawal of the seat belt becomes difficult.
Accordingly, to prevent such an end-lock due to the webbing sensor, a seat belt retractor has been proposed which cancels (disables) the original function of the webbing sensor for operating to inhibit withdrawal of the seat belt during full retraction of the seat belt (for example, see PTL 2 (Japanese Patent No. 3947064), incorporated by reference herein).
The seat belt retractor described in PTL 2 includes an inertia plate that swings in case of rapid seat belt withdrawal, a rotatable webbing sensor gear including internal teeth and external teeth, a webbing sensor pawl that is operated by swing of the inertia plate so as to engage with an internal tooth of the webbing sensor gear, and a gear rotation control pawl that engages with an external tooth of the webbing sensor gear to inhibit rotation of the webbing sensor gear.
In the seat belt retractor described in PTL 2, in a state in which the seat belt is withdrawn from the seat belt retractor by a predetermined length, the gear rotation control pawl engages with the external tooth of the webbing sensor gear to disable rotation of the webbing sensor gear. Thus, when the webbing sensor pawl is operated by swing of the inertia plate and engages with the internal tooth of the webbing sensor gear, the webbing sensor gear does not rotate. Hence, the original function of the webbing sensor is performed, and withdrawal of the seat belt is inhibited. Further, in a state in which the spool substantially fully retracts the seat belt, the gear rotation control pawl separates from the external tooth of the webbing sensor gear to allow rotation of the webbing sensor gear. Thus, even when the webbing sensor pawl is operated by swing of the inertia plate and engages with the internal tooth of the webbing sensor gear, the webbing sensor gear rotates and the spool is allowed to rotate in the seat belt withdrawing direction. Hence, the original function of the webbing sensor is cancelled. Therefore, withdrawal of the seat belt is enabled, and an end-lock is prevented. The seat belt retractor described in PTL 2 also includes a vehicle sensor.